Prime Chime Time

Here's your nightly math! Just 5 quick minutes of number fun for kids and parents at home. Read a cool fun fact, followed by math riddles at different levels so everyone can jump in. Your kids will love you for it.

Prime Chime Time

Of all the clocks in the world, the most famous might be Big Ben. It’s also the biggest clock, as you can guess from the name, and rests inside one of the tallest clock towers. Ever since 1859 this huge clock tower in London has been ticktocking the time and ringing every 15 minutes to remind us it’s there. Everything about this clock is huge. It actually has 4 clock faces, one on each side of the square tower, each one made of 312 pieces of glass. The machine itself that turns all those hands weighs 13 ½ tons — probably because the hands of the clocks are longer than you are! As you can see and hear in this video, the chiming is so loud that while inside the tower you have to wear ear protectors. And all those loud years add up: Big Ben has chimed over 8 million times in the last 150 years. We may have watches and phones that show the time, but Big Ben makes sure we’re paying attention.

Wee ones: If the clock chimes once at 1 pm and twice at 2 pm, how many times will it chime on the next hour?

Little kids: Big Ben has 4 clocks to turn, and each has a minute hand and an hour hand. How many hands does Big Ben turn? Bonus: You have to climb 334 steps to get to the top. If you’ve climbed all but 1, how many have you climbed?

Big kids: If the clock chimes every 15 minutes, how many times does it chime from 2 to 5 pm, including the start and finish? Bonus: The clock ticks (very loudly) only once every 2 seconds. How long does it take to tick 25 times? (In other words, the time between the 1st tick and the last).

The sky’s the limit: Now it’s prime time. If we write the time in digits, 2:35 is the first time after midnight with all different single-digit prime numbers. What is the last time before noon that this happens?

Answers:Wee ones: 3 chimes.

Little kids: 8 hands. Bonus: 333 steps.

Big kids: 13 times (4 per hour plus the extra at the other end). Bonus: 48 seconds, since there are 24 2-second chunks of time.

The sky’s the limit: 7:53 am. In short, you want to “use up” the biggest possible prime for the hour first, then the latest possible tens digit for the minutes, then the ones digit.

And thank you Catherine M. for sharing this cool video of facts about Big Ben!

About the Author

Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking while still in diapers, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.